Many applications require polarized light to function properly. One example of such an application are optical displays, such as liquid crystal displays (LCDs), which are widely used for lap-top computers, hand-held calculators, digital watches, automobile dashboard displays and the like. Another such application is task lighting configurations for increased contrast and glare reduction.
To produce polarized light, a light source is typically coupled with one or more absorptive polarizers. These polarizers use dichroic dyes which transmit light of one polarization orientation more strongly than the orthogonal polarization orientation. Dichroic polarizers are very inefficient, however, in that light of the orthogonal polarization is largely absorbed and is therefore unavailable for application illumination. For example, a typical dichroic polarizer transmits only about 35-45% of the incident light emitted by a standard display backlight. This inefficiency is a major disadvantage to dichroic polarizers, as the light which is absorbed is not available for the associated application. In an LCD display, for example, the absorbed light does not contribute to the illumination, and thus the overall brightness, of the LCD.
Vacuum deposited, thin film dielectric polarizers are not absorbing, as are dichroic polarizers, but do suffer other disadvantages, such as poor angular response and poor spectral transmission for non-designed wavelengths. In addition, they are conventionally coated onto stable substrates, such as bulk optical glass or polymer substrates, which render them too bulky and heavy for use in applications requiring light weight and small profile.
Current technology, for LCD illumination, makes no attempt at polarization control other than use of inefficient, dichroic polarizers. Current technology, for glare reduction in task lighting and vehicle displays, does not use polarizers at all due to the inefficiencies of dichroics, and the bulk and angle performance of vacuum deposited dielectric polarizers.